Cryptocrystalline

Crypto meaning “hidden” refers to a rock texture in which individual crystals are too small to be distinguished even using a standard petrographic microscope. Crystals are typically less than a few μm in size – any smaller and the texture would be considered amorphous. Among sedimentary terrestrial rocks, chert and flint are cryptocrystalline.

Cryptocrystalline (C) is one of the 8 types of chondrule textures as seen below.

Chondrule Textures. Image Credit: Antonio Ciccolella, commons.wikimedia.org